1. Field of the Invention
The present invention relates to a position detection apparatus for detecting the surface position of an object, an exposure apparatus having the position detection apparatus, a control method therefor, and a device manufacturing method.
The position detection apparatus of the present invention can be applied to, e.g., a surface position measuring apparatus for measuring a small distance by an electrostatic scheme. The exposure apparatus of the present invention can be applied to, e.g., a slit-scan exposure apparatus.
2. Description of the Related Art
As surface position detection apparatuses for semiconductor exposure apparatuses, position detection apparatuses which obliquely irradiate a semiconductor wafer, placed at a position where a mask pattern is to be transferred through a projecting lens, with light from a projector, and detect light obliquely reflected by the surface of the semiconductor wafer to detect the surface position are widely used. FIG. 9 is a schematic view of such a conventional surface position detection apparatus.
As shown in FIG. 9, illumination light emitted from the output end of an optical fiber 9 illuminates a pattern forming plate 11 through a condenser lens 10. The illumination light passing through the pattern forming plate 11 is projected onto the exposure surface of a wafer 5 through a lens 12, mirror 13, and projection objective lens 14, so the image of the pattern on the pattern forming plate 11 is formed on the exposure surface of the wafer 5 from an oblique direction with respect to an optical axis EX. The illumination light reflected by the wafer 5 is reprojected onto the light-receiving surface of a light-receiving device 18 through a condenser objective lens 15, mirror 16, and imaging lens 17. The image of the pattern on the pattern forming plate 11 is formed on the light-receiving surface of the light-receiving device 18. When the wafer 5 moves in the vertical direction, the image of the pattern moves to the left or right on the light-receiving surface 18. When an arithmetic circuit 19 calculates the position of the pattern, the surface position of the wafer 5 can be detected.
In the exposure apparatus, such a focus detection system has a plurality of measurement points in one shot (area to be exposed) of a wafer. A surface position z and tilt component (tilt) of the measurement shot are calculated by comparing the measurement results at the plurality of measurement points within the X-Y plane. Highly accurate focus position control is achieved by controlling a Zxc2x7tilt stage 8.
In recent years, a slit-scan exposure apparatus which exposes while holding a reticle and wafer conjugate with a projecting lens and scanning both the reticle and wafer to increase the exposure area has received a great deal of attention. In this exposure apparatus, a focus detection signal is directly used as a closed loop signal for controlling the posture of the stage. As the signal, a signal as smooth as possible, i.e., a signal averaged for an exposure area is necessary.
However, since the slit light projection scheme cannot measure position while uniformly illuminating a measurement surface of interest, the measurement areas always become discrete. In addition, experiments conducted by the present inventors have revealed that when a thin slit-like light beam irradiates the edge portion of a step, the reflected light is scattered to generate a large focus detection error.
This problem can be solved by using an electrostatic sensor as a focus detection sensor. An electrostatic sensor is more advantageous as a focus detection sensor of a slit-scan exposure apparatus than an optical sensor because it can almost uniformly average within the detection area, does not generate any focus detection error at an edge portion, and has a high response speed.
FIG. 10 is a view showing the principle of distance measurement by an electrostatic sensor. Referring to FIG. 10, a flat electrode 30 used for measurement is arranged near an object 31 to be measured. A high-frequency voltage is applied from an oscillator OS to the flat electrode 30. An ammeter AM is connected between the flat electrode 30 and oscillator OS. The ammeter AM and a measurement device 32 connected to the ammeter AM measure the magnitude of an AC current flowing to the flat electrode 30. The current measurement result is input to an arithmetic circuit 33. A distance d between the flat electrode 30 and the object 31 to be measured is measured by arithmetic processing by the arithmetic circuit 33.
Although the above-described surface position detection apparatus can obtain high accuracy in detecting the surface position of a substrate having a chip layout (pattern of a chip) compatible with the apparatus, no high accuracy can be obtained in detecting the surface position of a substrate having a chip layout incompatible with the apparatus.
In addition, when the shape of the wafer surface changes to a shape incompatible with the apparatus because of the repeated lithography process, the above-described surface position detection apparatus cannot accurately detect the surface position of the substrate.
The present invention has been made in consideration of the above situation, and has as its object to accurately detect the surface position of an object to be measured independently of the surface state of the object.
According to the first aspect of the present invention, there is provided a position detection apparatus for detecting a position of an object surface in a direction normal thereto, comprising at least two detection sections, a selection section for selecting at least one detection section from the at least two detection sections, and a measurement device for measuring the position of the object surface in the direction normal thereto using the detection section selected by the selection section.
In the position detection apparatus according to the first aspect, preferably, for example, each of the at least two detection sections has an electrode, and the measurement device applies an electrical signal containing an AC component to the electrode of the selected detection section to measure a distance between the electrode and the object surface.
In the position detection apparatus according to the first aspect, for example, the electrodes of the at least two detection sections preferably oppose different portions of the object surface.
In the position detection apparatus according to the first aspect, for example, the electrodes of the at least two detection sections are preferably in one plane.
In the position detection apparatus according to the first aspect, for example, the electrodes of the at least two detection sections are preferably concentric with each other.
In the position detection apparatus according to the first aspect, for example, the selection section preferably alternatively selects one detection section from the at least two detection sections.
In the position detection apparatus according to the first aspect, for example, the selection section determines the number of detection sections to be used for measurement.
In the position detection apparatus according to the first aspect, for example, the selection section preferably selects at least one detection section in accordance with a shape of the object surface.
In the position detection apparatus according to the first aspect, for example, preferably, the apparatus comprises at least two sets of the at least two detection sections, the selection sections, and the measurement devices, and further comprises an arithmetic section for calculating a tilt of the object surface on the basis of a measurement result by the at least two measurement devices.
According to the second aspect of the present invention, there is provided an exposure apparatus having a projecting lens for projecting a pattern onto a substrate, a stage which moves while supporting the substrate, a position detection section for detecting a position of a substrate surface in a direction of an optical axis, and a control section for controlling the stage on the basis of an output from the position detection section, the position detection section comprising at least two detection sections, a selection section for selecting at least one detection section from the at least two detection sections, and a measurement device for measuring a position of the substrate in a direction normal thereto using the detection section selected by the selection section.
In the exposure apparatus according to the second aspect, preferably, for example, each of the at least two detection sections has an electrode, and the measurement device applies an electrical signal containing an AC component to the electrode of the selected detection section to measure a distance between the electrode and the substrate surface.
In the exposure apparatus according to the second aspect, for example, the electrodes of the at least two detection sections preferably oppose different portions of the substrate surface.
In the exposure apparatus according to the second aspect, for example, the electrodes of the at least two detection sections are preferably in one plane.
In the exposure apparatus according to the second aspect, for example, the selection section alternatively selects one detection section from the at least two detection sections.
In the exposure apparatus according to the second aspect, for example, the selection section preferably determines the number of detection sections to be used for measurement.
In the exposure apparatus according to the second aspect, for example, the selection section preferably selects at least one detection section in accordance with a shape of the substrate surface.
In the exposure apparatus according to the second aspect, for example, the selection section preferably selects at least one detection section in accordance with a position of the stage or the substrate.
In the exposure apparatus according to the second aspect, for example, the selection section preferably selects the detection section to be used for measurement to measure the position of the substrate in a direction other than in a direction normal thereto on a scribing line of the substrate.
In the exposure apparatus according to the second aspect, for example, the selection section preferably determines the number of detection sections for measurement in accordance with the pattern formed on the substrate.
In the exposure apparatus according to the second aspect, for example, the selection section preferably determines detection sections to be used for measurement in accordance with a position of an exposure area on the substrate.
In the exposure apparatus according to the second aspect, for example, the selection section preferably determines the number of detection sections to be used for measurement to reflect, on the measurement result, a position of an exposure area on the substrate in the direction normal thereto where high resolving performance is required.
According to the third aspect of the present invention, there is provided an exposure apparatus having a projecting lens for projecting a pattern onto a substrate, a stage which moves while supporting the substrate, first and second position detection sections for detecting a position of a substrate surface in a direction of an optical axis, and a control section for controlling a tilt of the stage on the basis of outputs from the first and second position detection sections, each of the first and second position detection sections comprising at least two detection sections, a selection section for selecting at least one detection section from the at least two detection sections, and a measurement device for measuring a position of the substrate in a direction normal thereto using the detection section selected by the selection section.
In the exposure apparatus according to the third aspect, preferably, for example, each of the at least two detection sections has an electrode, and the measurement device applies an electrical signal containing an AC component to the electrode of the selected detection section to measure a distance between the electrode and the substrate surface.
In the exposure apparatus according to the third aspect, for example, the electrodes of the at least two detection sections preferably oppose different portions of the substrate surface.
In the exposure apparatus according to the third aspect, for example, the electrodes of the at least two detection sections are preferably in one plane.
In the exposure apparatus according to the third aspect, for example, the electrodes of the at least two detection sections are preferably concentric with each other.
In the exposure apparatus according to the third aspect, for example, each of the selection section of the first position detection section and the selection section of the second position detection section preferably selects a detection section such that both the detection section of the first position detection section and the detection section of the second position detection section, which are to be used for measurement, are positioned on an inner area of a width of the pattern projected by the projecting lens and a distance between the detection sections is maximized. Preferably, the substrate is exposed while projecting slit-shaped light onto the substrate through the projecting lens and moving the stage.
In the exposure apparatus according to the third aspect, for example, each of the selection section of the first position detection section and the selection section of the second position detection section preferably selects a detection section such that both the detection section of the first position detection section and the detection section of the second position detection section, which are to be used for measurement, are positioned inside a width of the pattern projected by the projecting lens on the substrate and a distance between the detection sections is maximized. Preferably, the substrate is exposed while projecting slit-shaped light onto the substrate through the projecting lens and moving the stage.
According to the fourth aspect of the present invention, there is provided a position detection method of detecting a position of an object surface in a direction normal thereto, comprising the selection step of selecting at least one detection section from at least two detection sections, and the measurement step of measuring the position of the object surface in the direction normal thereto using the selected detection section.
According to the fifth aspect of the present invention, there is provided a method of controlling an exposure apparatus having a projecting lens for projecting a pattern onto a substrate, a stage which moves while supporting the substrate, a position detection section for detecting a position of a substrate surface in a direction of an optical axis, and a control section for controlling the stage on the basis of an output from the position detection section, comprising the selection step of selecting at least one detection section from at least two detection sections, and the measurement step of measuring a position of the substrate in a direction normal thereto using the selected detection section.
According to the sixth aspect of the present invention, there is provided a method of controlling an exposure apparatus having a projecting lens for projecting a pattern onto a substrate, a stage which moves while supporting the substrate, first and second position detection sections for detecting a position of a substrate surface in a direction of an optical axis, and a control section for controlling a tilt of the stage, each of the first and second position detection sections comprising at least two detection sections, comprising the selection step of selecting at least one detection section from the at least two detection sections of the first position detection section and at least one detection section from the at least two detection sections of the second position detection section, and the measurement step of measuring the tilt of the substrate using the selected detection section of the first position detection section and the selected detection section of the second position detection section.
According to the seventh aspect of the present invention, there is provided a device manufacturing method comprising the steps of placing a substrate applied with a resist film on a stage of an exposure apparatus, selecting at least one detection section of at least two detection sections for measuring a position of the substrate in a direction of an optical axis and measuring the position of the substrate on the stage in the direction of the optical axis using the selected detection section, controlling the stage in accordance with a measurement result in the measurement step, forming a pattern on the substrate on the stage by exposure, and developing the substrate.
According to the eighth aspect of the present invention, there is provided a device manufacturing method comprising the steps of placing a substrate applied with a resist film on a stage of an exposure apparatus, selecting at least one detection section from each of two position detection sections each having at least two detection sections for measuring a position of the substrate in a direction of an optical axis and measuring a tilt of the substrate on the stage using the selected detection sections, controlling the tilt of the stage in accordance with a measurement result in the measurement step, forming a pattern on the substrate on the stage by exposure, and developing the substrate.
According to the present invention, the height or tilt of an object surface can be accurately measured independently of the surface shape of the object.
According to the ninth aspect of the present invention, there is provided a surface position detection apparatus which uses an electrostatic sensor having an electrode arranged on a surface to be measured, voltage application means for applying a high-frequency voltage between the electrode and the surface to be measured, and detection means for detecting a distance between the surface to be measured and the electrode on the basis of a value of a current flowing when the high-frequency voltage is applied between the electrode and the surface to be measured, the electrostatic sensor having a plurality of electrodes as the electrode, and selection means for selecting the electrode to be used.
According to the tenth aspect of the present invention, there is provided an exposure apparatus comprising the surface position detection apparatus for detecting a position of a surface to be exposed, and means for controlling the selection means in correspondence with a state of the surface to be exposed, whose surface position is to be detected.
According to the eleventh aspect of the present invention, there is provided a device manufacturing method using the exposure apparatus, comprising the steps of detecting a surface position of a substrate to be exposed while appropriately selecting an electrode to be used in each electrostatic sensor by the surface position detection apparatus of the exposure apparatus, and exposing the substrate while controlling the position of the substrate to be exposed on the basis of a detection result.
According to this arrangement, even when the chip layout of a print pattern of a wafer, i.e., the surface to be detected changes, an electrode to be used in each electrostatic sensor is selected in correspondence with the change. Distance measurement for surface position detection is performed by making the electrode oppose a preferable measurement position or measurement area. Since the electrode is simply selected by the selection means, the high-frequency voltage to be applied is common to the electrodes appropriately selected in each electrostatic sensor and, therefore, is constant for the electrodes. Hence, accurate surface position detection is performed in correspondence with a change in the surface to be detected.
According to a preferred aspect of the present invention, the electrostatic sensor comprises a variable distance measurement position electrostatic sensor having, as the selection means, switching means for switching the electrode to be used to change the measurement position or switching means for switching the number of electrodes to be used to change the measurement area.
The exposure apparatus is of a slit-scan type and comprises a surface position detection apparatus with the variable distance measurement position electrostatic sensor to detect tilt by pre-measurement for focus position control of the surface to be exposed, and means for controlling the switching means such that the measurement position by two electrodes of each of two different electrostatic sensors of the surface position detection apparatus is set on an outermost side within a scanning exposure width. Alternatively, the exposure apparatus comprises a surface position detection apparatus having the variable distance measurement position electrostatic sensor to detect a position in a direction of an exposure optical axis by pre-measurement for focus position control of the surface to be exposed, and means for controlling the switching means such that the surface position is not detected at a scribing line position.
The slit-scan exposure apparatus may comprise a surface position detection apparatus having the variable distance measurement position electrostatic sensor to detect the position in the direction of the exposure optical axis for pre-measurement for focus position control of the surface to be exposed. In this case, the exposure apparatus comprises means for controlling the switching means such that a large part of an exposure surface portion where high resolving performance is required is included in the measurement area.
The means for controlling the switching means can perform control on the basis of the exposure layout. Under the control, even when the exposure width becomes small, electrodes are selected such that the electrodes for calculating the tilt angle of the surface to be exposed are located within the width, thereby performing accurate focus position control. In addition, if a scribing line is located within the exposure slip, the electrode can be switched to cope with a plurality of chip patterns. In the surface position detection apparatus having the variable distance measurement position electrostatic sensor, the detection area to be averaged can be changed by switching the electrode to cope with a plurality of different chip layouts.
Further objects, features and advantages of the present invention will become apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings.